Variable length coaxial line section



June 26, 1956 v. H. RUMsEY VARIABLE LENGTH coAxIAL LINE SECTION Filed Aug. 18. 1948 3mm/vio@ VlCTOR H. RUMSEY wm Em ov mm mm 1 r mw A NN x i L JV ,f F/ y /H f fl Nw\ United States Patent VARIABLE LENGTH CAXIAL `LINE SECTION Victor H. Runisey, Columbus, Ghio, assigner to 'Minister ,of Supply in His Majestys Government of the United Kingdom oi Great Britain and Northern ireland, London, England Application August 18, 1948, Serial N o. .44,953

3 Claims. (Cl. S33-35) This invention relates to electrical energy transfer devices and more particularly to energy transfer devices capable of readily adjustable length yto permit vphysical position variation of pieces of apparatus which must'be electrically connected or to permit impedance determination by standing wave measurements.

In many applications of electrical energy transfer devices such as transmissionlines it may be desirable to have a section which may be varied in length over a considerable amount without introducing impedance misinatching of energy which may have frequency components at various points over a side frequency band. Such a device for example, would be very practical where it is desired to employ rigid type transfer couplingbetween electrical units which may themselves be non-rigidly mounted. Numerous instances of such installations are found on board ship where the electrical units are frequently shock mounted.

Another application of an adjustable length energy transfer apparatus is in high frequency impedance-.determination. The well known slotted line impedance measuring device-is not capable yof .extreme accuracy. An adjustable length line placed between the unknown impedance and a fixed probe .will permit standing wave measurements with a high degree of accuracy.

An object of the present 'mvention is to provide an adjustable length energy transfer apparatus capable of maintaining matched impedance operation over a wide frequency frange.

Another object of the present invention fis to provide an adjustable length energy transfer apparatus capable of maintaining a condition-ofimpedance.match vto a fixed section of transfer apparatus over a wide range-of length and` operating frequency.

Other and further objects and features of Vthe present invention will become apparent upon a .careful consideration of the accompanying drawing and following detailed description.

Fig. l shows in cross-section a typical device V`chosen to illustrate a preferred embodiment of :the features :of the present invention.

Fig. 2 shows a cross-section view of a modified portion of the apparatus of Fig. l.

According-to the Ifundamental concepts ,of Vthe present invention, a variable length energy transfer device is provided in which an intermediate impedance transforming section of transmission line having -a xed length is inserted between two mai-n transmission line sections. The intermediate section is xed with respect -to one of the main sections .and axially positionable with respect to the other. Compensation for -impedance variation at the junction of the sections is effectedby the impedance transforming properties of --the intermediate sectionwhich are chosen specifically to permit satisfactory matching over a wide frequency range.

With particular reference to Fig. l an energy transfer apparatus of variable length is shown which is preferably arranged .to receive an input signal at the end indicated in general by numeral '10 and deliver an `outputsignal atthe vend indicated in general by numeral 11. 'The structure .of the input section comprises .an inner conductor member 12 and an outer conductor member`13. The inner conductor is held in `place `within'the outer conductor by insulating spacers 14, 15 which arepreferably placed a distance of a quarter wavelength (at the mean frequency) apart to minimize their effect upon .the characteristic impedance yof the'line. Spacers `14 and 1'5 are` secured against longitudinal movement within conductor 13 by the cylindrical sleeves 1'6, 17, ,18 which preferably are of conductive material and whichtigh'tly engage the conductor 13. 'In asimilar .manner conductor 12 is secured against vlongitudinal motion bytightlyftting cylindrical conductive `sleeves 19 20, 21 which cooperate with spacers 14 and 15.

Into the left (in Fig. Vl) or open end of theinputline section is fitted an intermediate section of transmission line comprising the outer conductor 22 and the .inner conductor 23. .Conductors 22 and .23 are preferably securedto the `appropriate conductors of the input 4section .as by welding. .For ease of construction conductor 22 was placed as a slip fit vwithin sleeve 16 and conductor .23 as a slip lit on the outside of sleeve 19.

The intermediate line .section which is made up of 4sleeves22 and 23 is preferably equal in lengthto a Wavelength `at the mid-frequency of the .bandof electrical energy to be delivered. It is dividedfinto sections, kas by `a .variation .of .the dimensions of `one of the sleeves, ,to produce impedance matching to vcompensate for .inherent .impedance variation atfsuch points astthe junction with .the input section.

Thesecond end of the -intermediate line section slidably engages -an output .transmission line section for ;the vdeliverance Y.of energy to the endll thereof. This .output sectioncomprises Aanfinnerconductor member 24and an outerconductormember 2S. rlnner conductor 24-is.held in .place V'within `the outer conductor by 'the insulating .annular spacers 26, 27 which are secured .againstlongi- -tudinal motion within conductor `25 by :the .cylindrical :sleeves .23, 2-9, 3i) which -make va tight t against the inner Vsurface .of conductor25. Sleeves 28, .29, .3.0 :are preferably of conductive material to `permit the flow of electrical energy .on the .inner surfaces thereof. Inner Conductor 24 is `in turn securedagainst longitudinal motion by Athe spacers 26, 27 cooperating with the inner cylindrical Asleeves 31, 32, 33. SleeVes 31, 32, 33 are preferably of such a size as to have a ltig'ht fiton conductor 24 andliave a high conductivity for ellicient'ow of electrical energy-on Athe outer surfaces thereof.

Slidable contact is made between the inner surfacebf cylinder 30 and the enlarged rim portion Sii of section v22. Sirnilarlyfa slidable contact is made between the outer surface of cylinder V33 and the rim portion 35 of section 23. VIt is thus possible to vary the physical spacing between en'ds 1d and f-l over an appreciable distance and the lslidable contact mechanism will still lmaintain contact for eflcient energy transfer.

-Completelymatc'hed impedanceoperation is maintained where, in the process of energy transfer, standing waves are not present-in the out-putline section between en-d v11 and the -slidable contact portions 34, 35 and lin the input line -sect-ion ybetween end 10 and `the intermediate line section `having conductors l22 and '23. The realization of the firstrequirementfofat operation in the outputline section is generally vquite easy. `Such llat operation results naturally when the terminating impedance placed at end 11 is equal to the characteristic impedance of the output line section. On the other hand, the elimination of standing waves in the input section is quite a different matter. The discontinuities introduced by the abrupt change in diameter at the ends of sections 22 and 23 and by the intermediate line section itself necessitate special impedance matching.

This special impedance matching is provided within the intermediate section of line by a number of impedance matching sections and is of a simplified nature when the characteristic impedance of the output section is equal to that of the input section (Zo). The first of the impedance matching sections, that between points 36 and 37, is preferably equal to a quarter Wavelength and is of a characteristic impedance (A) less than (Zo). The centra] position of the intermedaite line section from 37 to 38, which is equal to a half wavelength, is then assigned a characteristic impedance (B) less than (A). The remaining portion of the intermediate section, that between point 38 and the sliding contact 35, is also ma-de of characteristic impedanceV (A). These impedance matching sections may be seen to comprise two double quarter wave transformers which Will be self-compensating over a wide frequency range.

With the device of Fig. 1, it is not possible to obtain a length variation of much more than /Zt of a wavelength. Where a large variation is desired, the intermediate section may be altered as shown in Fig. 2. The construction of the intermediate section of Fig. 2 differs from the comparable section of Fig. l only in the addition of the extra impedance matching portion 39--40- To effect this addition, the central half wavelength portion 37-38 of Fig. 1, was cut in the middle and the extra length section inserted. Upon removal of the annular insulating spacer 27, a greater adjustable length is obtained. There is no specific length restriction for portion 39-40.

For impedance determination, the unknown impedance may be placed at the output end 11 and a probe inserted into the input section at a convenient point thereof. Standing wave ratios may then be measured by varying the length of the line between the end 11 and the probe.

From the foregoing discussion it is apparent that considerable modification of the features of the present invention is possible and while the device herein described and the forms of apparatus for the operation thereof constitutes a preferred embodiment of the invention it is to be understood that the invention is not limited to this particular device and forms of apparatus and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

. What is claimed is:

1. An adjustable length high-frequency electrical energy transfer device, comprising, a rst end section of coaxial transmission line having inner and outer conductors, a rst sleeve of conductive material having an inside diameter slightly greater than the outside diameter of the inner conductor of the transmission line section and at least equal in length to one wavelength at the mean frequency of the energy and held in a fixed position relative to the rst end section, a second sleeve of conductive material of outer diameter slightly less than the inner diameter of the outer conductor of the transmission line and equal in length to that of the rst sleeve and held in a fixed position relative to the outer conductor, and a second end section of coaxial transmission line slidably engaging at selected portions thereof the inner surface and outer surface respectively of said rst and second sleeves whereby is permitted energy transfer between the first and second end sections of coaxial transmission line, two end portions of said first sleeve each one quarter wavelength long at the mean frequency of the energy and having equal but smaller diameters than the center portions thereof to maintain substantially matched impedance operation over a w'de frequency range.

2. An adjustable length high-frequency electrical energy transfer device, comprising: a first end section of coaxial transmission line having inner and outer conductors, a first sleeve of conductive material having an inside diameter slightly greater than the outside diameter of the inner conductor of the transmission line section and equal in length to one wavelength at the mean frequency of the energy and held in a fixed position relative to the end of the inner conductor, a second sleeve of conductive material of outer diameter slightly less than the inner diameter of the outer conductor of the transmission line and equal in length to that of the rst sleeve and held in a fixed position relative to the outer conductor, and a second end section of coaxial transmission line slidably engaging at selected portions thereof the inner surface and outer surface respectively of said rst and second sleeves whereby is permitted energy transfer between the first and second end sections of coaxial transmission line, two end portions of said first sleeve each one quarter wavelength long at the mean frequency of the energy and having equal but smaller diameters than the center portions thereof to form two back-to-back double quarter Wave impedance transformation sections to maintain substantially matched impedance operation over a wide frequency range.

3` An adjustable length highfrequency electrical energy transfer device, comprising: a first end section of coaxial transmission line in which the inner conductor is held from longitudinal motion by at least a short annular section lof insulating material placed a distance of an electrical quarter wavelength from the end thereof, a rst sleeve of conductive material of inside diameter slightly greater than the outside diameter of the inner conductor of the transmission line section, said sleeve being equal in length to one wavelength at the mean fre quency of the energy and held in a fixed position relative to the outer conductor, a second sleeve of conductive material of outer diameter slightly less than the inner diameter of the outer conductor of the transmission line, said second sleeve substantially equal in length to the iirst sleeve and held in a fixed position relative to the outer conductor, and a second end section of coaxial transmission line having an inner conductor of outer diameter permitting a slidable fit of high conductivity at the second end of the irst sleeve and an outer conductor of inner diameter permitting a slidable lit of high conductivity about the second end of the second sleeve to permit energy transfer between the ends of the coaxial transmission line, the inner conductor of the second end section of coaxial transmission line being held from longitudinal motion by at least a short annular section of insulating material placed a distance at least a electrical quarter wavelength from the end thereof, two end portions of said rst sleeve each one quarter wavelength long at the mean frequency of the energy and having equal but smaller diameters than the center portions thereof to form two back-to-back double quarter wave impedance transformation sections to maintain substantially matched impedance operation over a wide frequency range.

References Cited in the file of this patent UNITED STATES PATENTS 2,165,961 Cork et al. July 1l, 1939 2,280,728 Strieb Apr. 21, 1942 2,449,073 Iohannesen Sept. 14, 1948 2,518,665 Collard Aug. 15, 1950 2,564,007 Hochgraf Aug. 14, 1951 2,588,436 Violette Mar. ll, 1952 2,644,028 Bernet June 30, 1953 

